New Estrogen Receptor Found in Brains
Two years ago, graduate student Larry J. Young wouldn't have guessed that his investigation into the sex lives of lizards would lead him to an important region of the rat's brain.
Young and his colleagues at the University of Texas at Austin wanted to understand the role of the hormone estrogen in the sexual behavior of an all-female species of whiptail lizards, Cnemidophorus uniparens (SN: 5/30/87, p.348), and in a related, ancestral species. To do that, he planned to map the distribution of the molecular docking sites, or receptors, for estrogen in lizard tissue.
However, when he tried to develop genetic probes to help him pinpoint these receptors, he wound up with some baffling sequences of nucleotides, the chemical building blocks whose order specifies a protein. Genes typically contain meaningful regions, called exons, with noncoding sequences of nucleotides shoved in between the exons. Messenger RNA molecules, which transfer a gene's information to protein-building machinery, form by matching their nucleotides to the sequences in exons, ignoring the noncoding sections.
The beginning and end of some of the messenger RNA sequences that Young observed matched perfectly the beginning and end of RNA for the human estrogen receptor. But this lizard RNA was missing something in the middle. After much head-scratching, Young figured out that as the lizard RNA formed, it ignored or somehow deleted the information from the fourth exon. Instead it consisted of exons 1 to 3, followed by exon 5.
As a result, says Young, this RNA leads to a newly identified estrogen receptor -- one that exists primarily in the brain.
Knowing that many biomedical researchers wouldn't care much about a new lizard receptor, David Crews, Young's advisor, decided they should find out whether this form of the receptor exists in rats as well. "It would imply evolutionary conservation of this form, which [would] cause us to think that this form would be important," says James K. …